The invention relates to a longitudinally plungeable constant velocity universal ball joint having an outer joint part with inner first straight ball tracks, an inner joint part with outer second straight ball tracks, with each set of associated first and second ball tracks accommodating one ball of a plurality of torque transmitting balls and with the center lines of at least part of the associated first and second ball tracks intersecting one another while crossing the axes of the outer joint part and inner joint part respectively at opposed angles of equal size, and further having an annular cage which comprises a plurality of windows corresponding to the plurality of balls, each window accommodating one of the balls, with the cage having an outer contour which comprises a central spherical surface portion centering the cage relative to the outer joint part when the joint is in the aligned position, and adjoining conical faces half the opening angle of which corresponds to half the maximum articulation angle .beta./2.
Joints of this type are used in drivelines of motor vehicles to achieve long plunging distances, for example in driving halfshafts at the inner end of the differential. They are described in DE-GM 1 876 790 for example.
In a developed view, the intersecting tracks may extend parallel relative to one another in the inner joint part and outer joint part or they may form opposed angles of equal size with the axial direction.
Joints of this type must be produced with tracks intersecting one another in accordance with the definition. However, it is also possible to provide axis-parallel tracks which complement the intersecting tracks serving to control the balls on to half the plunging distance and on to the angle-bisecting plane and thus to control the cage in the case of plunging movements and articulation movements.
The inner contour of the outer joint part which serves for axially guiding the cage is entirely cylindrical and does not permit any other design possibilities. The shape of the cage and the outer contour of the inner joint part does permit different designs, with certain design objectives not being compatible with one another. For strength reasons it is desirable for the wall thickness of the cage to be as great as possible. On the other hand, to increase the torque capacity attempts have to be made to provide the tracks in the inner joint part with as much depth as possible. These two requirements, when put into practice, restrict one another. Furthermore, it is desirable on the one hand to provide joints with as large an articulation angle as possible while at the same time aiming at a long plunging distance. However, as in a fully extended and articulated joint the points of intersection on the axes of the respective components are no longer located in the component center, the maximum possible articulation angle is reduced when extending the joint.
A further design criterion refers to the contact of the ball in the cage window. Care has to be taken to ensure that the point of contact is not too close to the inner edge of the cage to prevent material from breaking off, especially after the occurrence of slight wear.
There are already prior art joints of the initially mentioned type wherein the outer contour of the cage consists of a central spherical disc and adjoining conical portions. In a longitudinal section, the outer contour can be described as being "roof-like". Half the opening angle of the cone corresponds to half the articulation angle of the joint, which is due to the fact that relative to each of the two joint components, i.e. the outer joint part and inner joint part, the cage carries out only half the articulation angle.
Furthermore, it is the case with such prior art joints that the outer contour of the inner joint part also comprises two conical portions which, as a rule, are connected to one another by a simple turned central cylindrical portion. Under conditions of maximum joint articulation, the conical portions of the cage cooperate with the cylindrical inner face of the outer joint part and the conical portions of the inner joint part cooperate with the cylindrical inner face of the ball cage in that they limit the articulation angle and the plunging distance by contacting one another.
It is the object of the present invention to improve a joint of the above-mentioned type without substantially reducing its strength in that at a given maximum articulation angle, the axial plunging distance can be improved and that, with an unchanged articulation angle and axial plunging distance, the torque transmitting capacity of the inner joint part can be increased.